1. Field of the Invention
The present invention relates to an atmospheric pressure compensation device operable in response to variation in the atmospheric pressure level. The device is useful, for example, to control the air-fuel ratio of a mixture produced by a carburetor of an internal combustion engine or the ignition timing of the engine in accordance with the atmospheric pressure level at which the engine is operated. The invention will be described hereunder in connection with an internal combustion engine, but it is to be understood that the application of the present invention is not limited to this class of art.
2. Description of the Prior Art
In general, the carburetor of an internal combustion engine has a primary main nozzle, a secondary main nozzle, a slow circuit and a power nozzle. The rates of the fuel flow through these nozzles and circuit are controlled dependent on the venturi vacuum, the intake manifold vacuum and the rates of air supplies through respective air bleeds to thereby adjust the air-fuel ratio of an air-fuel mixture produced by the carburetor. The atmospheric pressure is at a low level at a high altitude. Thus, the air supplied through the air bleeds into the carburetor is of a density smaller or lower than that available at a low altitude or on the so-called "lowland." The supply of the low-density air causes an enrichment of the air-fuel mixture with a resultant increase in the emission of the harmful components of the engine exhaust gases.
In an attempt to eliminate this problem, there has been deviced a carburetor in which the air flows through air bleeds are controlled by needle valves which are actuated by a pressure responsive bellows member of members. However, because the carburetor air bleeds are of diameters ranging from 0.5 to 1.0 mm, the needles to be associated with such very small holes or openings must be machined extremely precisely. In addition, the needle valves must be moved over relatively long strokes. In the case where a single bellows member is used to actuate a plurality of needles associated with respective air bleeds of the carburetor, a very complicated mechanism, such as a link work, is needed to operatively connect the bellows member to the needles. The link work must be precisely made so as to accurately transmit deformation of the bellows member to respective needles.